CO.sub.2 lasers typically contain a mixture of gases such as carbon dioxide, nitrogen and other gases An electrical discharge between a pair of electrodes within the laser cavity induces the lasing of the CO.sub.2 and also dissociates the CO.sub.2 into CO and O.sub.2. This dissociation of CO.sub.2 tends to reduce the volume of the CO.sub.2 within the laser, resulting in the gradual decrease in the output power of the laser and, possibly, in the complete failure of the laser after a period of time
In order to replenish the CO.sub.2 it has been known to provide an external gas canister of CO.sub.2. However, in some applications, such as military applications, such an external gas canister may be undesirable.
It has also been known to provide a catalyst within the laser cavity to recombine the dissociated CO and O.sub.2 inasmuch as CO and O.sub.2 do not readily recombine at room temperatures or at typical laser operating temperatures. A variety of catalysts have been known which promote this reconstitution of CO.sub.2 from CO and O.sub.2. An example of such a catalyst is metallic platinum (Pt) in wire form which is resistively heated to a temperature of about 1000.degree. C. It has also been known to recombine CO and O.sub.2 by pumping the laser gas through a bed of hopcalite (60% MnO.sub.2, 40% CuO, and trace quantities of other oxides), the hopcalite typically being provided in granular or powder form. However, a significant pressure drop may occur within such a bed of hopcalite if it is required that the laser gas be pumped through the bed. Also, hopcalite often requires periodic treatment in order to maintain its activity and must also be suitably contained such that the powder does not contaminate the inner surface of the laser cavity.
In a metallic platinum catalyst it is known that the number of CO.sub.2 and O.sub.2 molecules that are recombined to CO.sub.2 during a given interval of time is directly related to the surface area of the catalyst in contact with the molecules and, also, is exponentially related to the temperature of the platinum Thus, an increase in the surface area results in a significant decrease in the temperature required to accomplish a desired CO.sub.2 recombination rate.
Conventional methods of heating catalysts include upstream heating of the laser gas and direct thermal contact of the catalyst structure with an embedded heating element. The upstream heating of laser gas may be undesirable in some applications due to subsequent heat removal operations possible, inefficiency in heat transfer, and possible structural complexity and increased cost. Direct thermal contact of the catalyst structure with an embedded heating element may also prove disadvantageous due to inefficient thermal transport between the element and the catalytic structure and the difficulty in implementing this technique in a compact geometry.
It is therefore an object of the invention to provide a catalytic structure which employs a coating comprised of a catalytic material deposited upon an electrically conductive ceramic substrate, the substrate being resistively heated in order to elevate the catalytic coating to its activation temperature.
It is a still further object of the invention to provide a catalyst for a CO.sub.2 laser having a high catalytic activity per unit volume at a reduced operating temperature or a minimum power requirement, the catalyst having a resistively heated substrate for elevating a catalytic coating to a desired temperature.
One further object of the invention to provide a catalyst for a CO.sub.2 laser having a high catalytic activity per unit volume at a reduced operating temperature or input power requirement, the catalyst having a resistively heated ceramic substrate for elevating a catalytic coating to a desired temperature, the catalyst further having a temperature control coupled thereto for maintaining the coating at the desired temperature.